When I had one, it had no heater. After spending a December in Grand Canyon, in the snow, we found that the small heater fan we used was worthless. We froze at night. For the future, I purchased and installed an oversized Propane heater (with Stand) and propane hoses and fittings to tap into the propane line that went to the stove. Unfortunately, we never camped in that much cold again, but the heater was nice to have anyway.
We also installed privacy curtains on either side next to the beds to allow more privacy especially as the kids were getting older and they needed privacy as much as we did. It was in the plans, but I never did get around to adding a 2nd battery. In retrospect, most of our camping we had electricity so we didn't really need a 2nd battery.
Mathematically speaking what we paid for the popup, doing any mods that were more expensive than that (gutting or severe remodeling) in time or money didn't make sense to us. We ended up selling it. A few years later we bought a Travel Trailer, then the big fifth wheel we have now and with the larger price tag it did make sense for some of those mods but I think that's for another topic.
I do admire others who have spent much time and money redoing, refurbishing, or fixing up some of these old trailers and popups - those are labors of love, which unfortunately I do not share. But I like looking at what others have done.
I haven't done major mods to my small truck camper; just some improvements such as creating a removable cold weather insulation cover that may be attached though the vinyl parts with velcro (my wife is the genius in this area!)
when I had one, I connected the drains from the shower and the sink and fixed the end so that I could drain it into a sewer or a gray water tank. Also, built a rack that set on the top and was held in place by ratchet starps for holding ice coolers and wood. If anyone would like to know how this was done send me a PM
I would suggest taking a look at Ruides smugmug gallery He Ruide's Photos
he has been away from the forums for over a year now so I don't know how much longer it will be there ,,, he has some great ideas and lots of pics to show what he has done
We just added a smoke alarm to our PopUp camper as it did not have on we used a smaill 9 volt battery type with a metal bracket and a rare earth magnet attaching it to one of the metal ceiling support ribs
WE bought a 1986 jayco popup last year. First thing we did was replace the canvas, did I mention we paid 500 dollars...yikes. There were 4 bench seats and 2 tables, and 2 slide out beds. 2 of the benches and one table was rotted, we yanked it. The heater does not work, still looking for parts. The cabinet that housed the sink and cooktop was also rotten...my hubs built a new one. The remaining table was painted with chalk paint, good if it rains and you have kids. Wipe it off and good to eat on. Since we can not haul 2 trailers in our state we needed a way to transport our quads. The hubs and his work buddys modified the trailer itself... bigger axel for added weight and also a bigger wheel. They extended both sides of the trailer about 3 feet and put plywood on it for the quads to sit on. The camper has no water tank or ac, everything was gutted to be as light as possible , and we still come in under weight with quads loaded. Next project...replacing the wood planks around the top.